Now, you will need to turn 770 mmHg to pascales.
This is the way:
760mmHg is 101325Pa that would meen that 770mmHg is 100010Pa.
80oC needs to be turned to kelvines. How? Look:
T = t + 273.15K, that is:
T = 80 + 273.15
T = 353.15K
We have V, so we will again, use pV=nRT
V = 0.25L = 0.25dm3 = 0.00025m3
Just in this case, we will need to calculate n (number of moles).
n = pV/RT
n = 100010*0.00025/8.314*353.15
n = 0.008515mol
Form first equation (2Mg + O2 --> 2MgO) we can see that 2mol of MG reacts with 1mol of O2.

On helping with questions: Any and all assistance given to homework assignments or textbook style exercises should be given only after the questioner has shown some effort in solving the problem. If no attempt is made then the questioner should be asked to provide one before any assistance is given. Under no circumstances should complete solutions be provided to a questioner, whether or not an attempt has been made.

Thanks everyone (Samba especially)! I 'completed' the assignment last week - Looks like I got one right. I just guessed though because I couldn't figure out how to find the amount of moles to use in the PV=nRT equation. I'm still pretty fuzzy about that but thankyou so much Samba your step by step helped clear it up a little bit for me!

Sorry, I didn't know I was supposed to show my work. Next time I will, sorry.